The present invention relates to biodegradable gels which act as superabsorbing sponges. More particularly, the gel of the invention has as high, or higher, liquid and saline uptake than the polyacrylate superabsorbers now being used while having the advantage of being completely biodegradable.
Biodegradability has become a necessity in society in the last few years. As more and more products are made disposable, the waste problems associated with these disposables have become increasingly important. One example of this is the disposable diaper field. Until a few years ago, disposable diapers, though convenient, had not received widespread use because the amount of liquid which could be absorbed was limited. This limitation lead to use of the diapers for extraordinary circumstances but they were not feasible for most people on a day-to-day basis because of the leakage and resulting diaper rash problem. In order to solve these problems, the diaper manufacturers first used very thick diapers, placing large amounts of fiber such as cellulose in the diaper to act as a liquid, primarily saline and urine, absorber. These bulky diapers still had limitations on the amount of liquids they could retain while the bulk made them uncomfortable for the infants to wear.
The first major improvement in the disposable diaper field was the addition of the so-called "superabsorbers" as liquid traps. These superabsorbers are primarily polyacrylate particles which are placed in the diaper in loose form or are entrapped among cellulose fibers. These polyacrylate particles absorb large quantities of water by swelling and acting as individual pseudo-sponges. Since the amount of saline and urine which can be absorbed by these superabsorbers is so much greater than cellulose or other natural fibers, very thin diapers could be used, minimizing the problems to infants and making disposables the diaper of choice. The polyacrylate gel beads move freely relative to each other and form large spaces between each other. However, once fully hydrated, these polyacrylate superabsorbers tend to clump, causing a lumpy diaper and discomfort to the infant.
In addition to the use in diapers, the superabsorbers have other uses. Many other items which are used for absorption of liquid are a fertile ground for use of the superabsorbers. However, the polyacrylate superabsorbers have one major disadvantage; they are not biodegradable. This means that the diapers and all other products made using these superabsorbers are not degraded for decades; in fact, they need hundreds of years to breakdown. This leads to the aforementioned waste problem. Another disadvantage of the polyacrylates is that they absorb maximally at 0% saline while urine and most body fluids are about 0.15 N saline.
Materials which absorb liquid and are biodegradable such as those of the present invention have other possible uses as well. The entrapment of particles, including macromolecules such as hemoglobin and cells such as erythrocytes, is particularly important for feminine napkins and similar products. Superabsorbers have not made a great dent in this field even though they have the necessary liquid absorption because they cannot entrap large particulates.
Another possible use for a biodegradable material which will entrap liquid and/or particles is as a sustained release vehicle. In certain instances, the molecules to be delivered can be part of the structural material of the sponge itself. Most materials which are presently being tested as sustained release vehicles, e.g., microcapsules, liposomes and related capsular type products, have substantial costs and time associated with their manufacture. The ability to make a product in situ, apply it to a given area, and then let it degrade under ordinary conditions to release entrapped material, would solve many problems.
A further use of a gel which entraps liquids and particles is as a biological protective barrier. For example, a gel which entraps bacteria as it is hydrated, or prevents their passage once formed, can be used as a wound dressing, protecting the wound from bacteria while allowing air flow and/or free flow of liquid to the injury. A further use is in a diaper where coliform bacteria can breakdown urea in urine to ammonia, changing the pH and promoting diaper rash.
Accordingly, an object of the invention is to provide a biodegradable material that has high uptake for water and saline.
Another object of the invention is to provide a biodegradable carrier or sustained release delivery system for drugs and other molecules.
A further object of the invention is to provide a material and method for entrapment of particulates such as erythrocytes and protein molecules such as hemoglobin.
A still further object of the invention is to provide a protective barrier which prevents the passage of particles such as bacteria or macromolecules, e.g., for use as a wound bandage.
These and other objects and features of the invention will be apparent from the following description.